Heat Pump Circuit for Mercury Capture in Moist Gas
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Solution Overview
Problem
Existing methods for removing mercury from moist gaseous effluents, such as those from natural gas, are inefficient due to capillary condensation issues, which reduce the performance of mercury guard beds and lead to energy-intensive solutions like superheating, and often result in mercury contamination upstream of the treatment process.
Innovation Solution
A process integrating a heat pump circuit with a heavy metal capture mass to dehumidify the gas, maintaining a relative humidity below 90% and avoiding capillary condensation, using metallic sulphides or elemental sulphur as active phases on porous supports like aluminas or activated carbon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gas is heated to high temperatures to avoid capillary condensation, then the mercury capture performance is improved, but the energy consumption increases substantially
Solution Approach 1:
The invention changes the temperature parameter of the gas stream to maintain it above the dew point temperature, thereby preventing capillary condensation while avoiding excessive energy consumption. By controlling the temperature within a specific range rather than using high-temperature superheating, the system achieves effective mercury capture with reduced energy input.
Solution Approach 2:
The invention introduces a heat exchanger as an intermediary device to transfer heat from the hot effluent gas to the incoming moist gas. This intermediary heat transfer mechanism allows temperature control to prevent capillary condensation without direct high-energy heating, thereby improving energy efficiency while maintaining mercury capture performance.
2Quantity of substance
If traditional drying methods are used before mercury capture, then the moisture content is reduced, but the system complexity and cost increase
Solution Approach 1:
The heat exchanger serves multiple functions: it preheats the incoming gas to prevent capillary condensation, recovers energy from the effluent stream, and eliminates the need for separate drying equipment. This multi-functionality reduces system complexity while effectively controlling moisture content to protect the mercury capture bed.
Solution Approach 2:
The invention merges the heating function into the existing process stream by using the effluent gas itself as the heat source. Instead of adding separate drying or heating equipment, the system combines the thermal management functions within the existing flow path, thereby reducing device complexity and operational cost.
3Productivity
If the capture mass is exposed to high moisture content gas, then the gas flow continues uninterrupted, but the capture mass performance deteriorates due to capillary condensation
Solution Approach 1:
The system performs preliminary heating of the incoming gas before it enters the mercury capture bed. By preheating the gas to above its dew point temperature, the system prevents capillary condensation from occurring within the capture mass, thereby protecting the capture mass performance while allowing continuous gas flow through the system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces mercury concentrations in the gas with minimal energy expenditure, maintaining guard bed performance and preventing upstream contamination, while being more cost-effective than traditional methods.
Implementation Method 1
the presence of water at high moisture contents in the vapour form in the gas to be treated may cause the appearance of capillary condensation phenomena on the porous supports used
Implementation Method 2
heating the moist gas by heat exchange with a compressed heat transfer fluid obtained in step e) in order to obtain a condensed heat transfer fluid and a gas reheated to a temperature Tc
Implementation Method 3
The impurity to be eliminated, in this case mercury, is then irreversibly retained, preferably by chemisorption, within or at the surface of the capture mass
Implementation Method 4
elemental sulphur S reacts irreversibly with elemental mercury, Hg°, as follows: Hg°(g/l)+S(s)→HgS(s)
Implementation Method 5
heating the moist gas by heat exchange with a compressed heat transfer fluid obtained in step e)
Implementation Method 6
compressing the vaporized heat transfer fluid obtained in step d) in a manner such as to obtain a compressed heat transfer fluid
Data Source
AI summary
Capturing at least one heavy metal, from mercury and arsenic, contained in a moist gas comprising water vapor, by the following steps:a) heating the moist gas by heat exchange with a compressed heat transfer fluid obtained in step e) in order to obtain a condensed heat transfer fluid and a gas reheated to a temperature Tc;b) bringing the reheated gas into contact with a heavy metal capture mass in order to obtain a gas depleted in heavy metal;c) decompressing the cooled heat transfer fluid;d) cooling the gas depleted in heavy metal by heat exchange with the heat transfer fluid produced in step c) in order to obtain a cooled gas at a temperature Tf, the heat transfer fluid being vaporized;e) compressing the vaporized heat transfer fluid in a manner such as to obtain a compressed heat transfer fluid, the compressed heat transfer fluid being recycled.